This invention relates to a plasma addressed liquid crystal device employing fiber spacers.
U.S. Pat. No. 5,077,553 discloses apparatus for addressing data storage elements. A practical implementation of the apparatus shown in U.S. Pat. No. 5,077,553 is illustrated schematically in FIG. 1 of the accompanying drawings.
The display panel shown in FIG. 1 comprises, in sequence from below, a polarizer 2, a channel member 4, a cover sheet 6 (commonly known as a microsheet), a layer 10 of electro-optic material, an array of parallel transparent data drive electrodes (only one of which, designated 12, can be seen in the view shown in FIG. 1), an upper substrate 14 carrying the data drive electrodes, and an upper polarizer 16. In the case of a color display panel, the panel includes color filters (not shown) between the layer 10 and the upper substrate 14. The panel may also include layers for improving viewing angle and for other purposes. The channel member 4 is typically made of glass and is formed with multiple parallel channels 20 in its upper main face. The channels 20, which are separated by ribs 22, are filled with an ionizable gas, such as helium. An anode 24 and a cathode 26 are provided in each of the channels 20. The channels 20 are orthogonal to the data drive electrodes and the region where a data drive electrode crosses a channel (when viewed perpendicularly to the panel) forms a discrete panel element 28. Each panel element can be considered to include elements of the layer 10 and the lower and upper polarizers 2 and 16. The region of the upper surface of the display panel that bounds the panel element constitutes a single pixel 30 of the display panel.
When the anode 24 in one of the channels is connected to a reference potential and a suitably more negative voltage is applied to the cathode 26 in that channel, the gas in the channel forms a plasma which provides a conductive path to the reference potential at the lower surface of the cover sheet 6. If a data drive electrode is at the reference potential, there is no significant electric field in the volume element of electro-optic material in the panel element at the crossing of the channel and the data drive electrode and the panel element is considered to be off, whereas if the data drive electrode is at a substantially different potential from the reference potential, there is a substantial electric field in that volume element of electro-optic material and the panel element is considered to be on.
It will be assumed in the following description, without intending to limit the scope of the claims, that the lower polarizer 2 is a linear polarizer and that its plane of polarization can be arbitrarily designated as being at 0xc2x0 relative to a reference plane, that the upper polarizer 16 is a linear polarizer having its plane of polarization at 90xc2x0, and that the electro-optic material rotates the plane of polarization of linearly polarized light passing therethrough by an angle which is a function of the electric field in the electro-optic material. When the panel element is off, the angle of rotation is 90xc2x0; and when the panel element is on, the angle of rotation is zero.
The panel is illuminated from the underside by an extended light source 34 which emits unpolarized white light. A rear glass diffuser 18 having a scattering surface may be positioned between the light source and the panel in order to provide uniform illumination of the panel. The light that enters a given panel element from the source is linearly polarized at 0xc2x0 by the lower polarizer 2 and passes sequentially through the channel member 4, the channel 20, the cover sheet 6, and the volume element of the electro-optic material toward the upper polarizer 16 and a viewer 32. If the panel element is off, the plane of polarization of linearly polarized light passing through the volume element of electro-optic material is rotated through 90xc2x0, and therefore the plane of polarization of light incident on the upper polarizer element is at 90xc2x0. The light is passed by the upper polarizer element and the pixel is illuminated. If, on the other hand, the panel element is on, the plane of polarization of the linearly polarized light is not changed on passing through the volume element of electro-optic material. The plane of polarization of light incident on the upper polarizer element is at 0xc2x0 and therefore the light is blocked by the upper polarizer element and the pixel is dark. If the electric field in the volume element of electro-optic material is intermediate the values associated with the panel element being off and on, light is passed by the upper polarizer element with an intensity which depends on the electric field, allowing a gray scale to be displayed.
In a practical implementation of the PALC display panel, the channel member 4 is etched back around the area in which the channels are formed in order to provide a plateau 36 in which the channels 20 are formed, and the cover sheet 6 is secured to the channel member by an endless frit bead 38 in a rabbet 40 extending around the periphery of the plateau. An upper substrate assembly, including the upper substrate 14 and the data drive electrodes 12 carried thereby, is attached to the channel member 4 by means of a glue bead 42.
It is important to proper functioning of the PALC device that the cover sheet be spaced from the channel substrate at least along the channels, to allow a plasma chamber to be defined between the cover sheet and the channel substrate. In accordance with the prior art, this spacing is provided by the ribs that define the plasma channels.
The channel substrate shown in FIG. 1 is manufactured by a subtractive process, in which a glass plate is selectively etched to form the channels. Possible disadvantages of the subtractive process are that the etching operation is expensive and imposes constraints on the cross-sectional shape of the channels. Further, it has been found difficult in practice to form the channel electrodes otherwise than by use of evaporative or sputter deposition and photolithographic processes.
Another known technique for forming the channel substrate of a PALC panel employs an additive process, in which the channel electrodes are deposited on a substantially flat surface of a glass plate and the ribs are then built up on the glass plate by screen printing. The additive process is time consuming because numerous printing stages are needed to build up the ribs, and it is difficult because of the need for accurate registration of successive printing screens. Further, the ribs are not of uniform height and steps must be taken to bring the ribs to uniform height before the cover sheet is applied.
The conventional processes are subject to disadvantage not only because of difficulty in manufacturing the channel substrate but also because of the possibility of damage to the cover sheet during assembly of a panel. Thus, the ribs have relatively sharp edges and there is a possibility that stresses induced in the cover sheet at the sharp edges will damage the cover sheet. Further, the tops of the ribs are flat and there is a possibility that hard particles, such as glass shards, will be trapped between the tops of the ribs and the cover sheet and that stresses induced in the cover sheet by the hard particles will damage the cover sheet.
In accordance with the invention there is provided an article of manufacture comprising a transparent plate having a substantially flat upper surface, and an array of substantially parallel spaced fiber segments attached to the upper surface of the transparent plate.